Atmospheric pollution generated by exhaust emissions from conventional gasoline or diesel powered internal combustion engines is a well documented problem. One recognized method of reducing noxious emissions is to replace the conventional fuel with a cleaner burning alternative fuel. For example, U.S. Pat. Nos. 4,711,223 and 4,635,608 issued to Carroll teach an alcohol fueled engine. Similarly, U.S. Pat. No. 4,112,875 issued to Laumann et al. discloses a hydrogen-oxygen fueled engine.
A problem with such alternative fuels is that they generally have less energy per unit volume than gasoline or diesel fuel, and therefore the power available from alternatively fueled engines is often reduced. To minimize the effects of this problem, designers have proposed to run such engines on a mixture of the alternative fuel with gasoline. See, for example, U.S. Pat. No. 4,995,367 issued to Yamauchi et al. Yamauchi teaches a system for controlling both fuel injection and ignition timing in an internal combustion engine operating on a fuel mixture such as gasoline and methanol. Similarly, U.S. Pat. No. 4,876,988 issued to Paul et al. teaches a combined fuel engine in which an auxiliary fuel such as methanol, ethanol or liquified natural gas high in hydrogen may be injected in various proportions with a conventional fuel. See also, U.S. Pat. No. 4,865,001 issued to Jensen which teaches the use of natural gas to supplement conventional diesel fuel. As disclosed by Jensen, a gaseous fuel injector valve is regulated according to certain sensed engine operating parameters, including the gaseous fuel temperature.
A problem with these supplementary systems is that they generally require a separate fuel transportation system for the alternative fuel. These transportation systems are often duplicative of those already in place for the transport of gasoline or diesel fuel, and thus increase the weight and cost of the vehicle due to the use of redundant parts. See, for example, U.S. Pat. No. 4,495,930 to Nakajima which discloses an internal combustion engine which utilizes separate gasoline and alcohol fuel injectors, as well as separate fuel transportation systems. As disclosed by Nakajima, the sets of injectors are separately controlled by a control system which outputs separate pulse width injection command signals. U.S. Pat. No. 5,092,305 to King discloses a fuel control system in which the fuel control signals generated by a primary fuel control computer are modified by an alternative fuel control module and are used to activate an independent fuel control valve to supply an alternative fuel to the engine.
One way of reducing the number of redundant parts when using an alternative fuel has been proposed by U.S. Pat. No. 4,922,862 to Cassacci. Cassacci discloses a system for supplying different fuels such as liquid petroleum gas or compressed natural gas to Otto engines with electronic fuel injection. As disclosed by Cassacci, the original injection nozzle and electronic control box are used, and a signal multiplier is added between the injection nozzle and the control box. The signal multiplier modifies the parameters leading the control box in accordance with a constant correction value to control the quantity of gas injected and to advance the spark plug ignition.